What was found
IMMEDIATELY AFTER TAKEOFF, THE COCKPIT BEGAN TO FILL WITH SMOKE. AFTER TURNING COCKPIT PACK OFF, SMOKE SEEMED TO DISSIPATE. COMPLIED WITH A LIMITED BORESCOPE INSPECTION OF THE APU IMPELLER. NO DEFECTS NOTED. COMPLIED WITH APU OPERATIONAL CHECK IAW MM 49-10-00. OPS CHECKS GOOD. ACCOMPLISHED NJA FORM TC-750-21-120801M R1 ENVIRONMENTAL CONTROL SYSTEM (ECS) DUCT BURNOUT AND REMOVED AND REPLACED THE COALESCHER BAGS, OPS CHECKED GOOD.